JP2008268066A - Ultrasonic vortex flowmeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic vortex flowmeter for measuring a flow rate of a fluid to be measured by detecting a Karman vortex generated on a downstream of a vortex shedder by ultrasonic waves while determining bubbles. <P>SOLUTION: A signal of the Karman vortex 17 from a filter amplifier circuit 30 is input in a bubble detection part 61 through an A/D conversion part 60. An amplitude value of the A/D converted vortex signal is constantly monitored whether it exceeds a threshold (stored in a memory 44 on each aperture of flowmeters). When the value exceeds the threshold, it is determined that the bubbles are mixed, and the determination is output to a frequency setting part 42. The frequency setting part 42 sets a cut-off frequency of a bandpass filter part 38 for passing the vortex signal, based on data stored in the memory 44, and based on a frequency of the vortex pulse signal measured by a counter part 40. In a flow rate operating part 46, the vortex signal is converted into a pulse sequence and is integrated to compute a flow rate to output a flow rate signal to an output terminal 47. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an ultrasonic vortex flowmeter, and in particular, transmits ultrasonic waves into a fluid to be measured, and detects Karman vortices generated downstream of the vortex generator while detecting bubbles to detect the flow rate of the fluid to be measured. The present invention relates to an ultrasonic vortex flowmeter that measures the above.

In general, ultrasonic flowmeters measure the flow rate of pure water at semiconductor factories, measure the flow rate of washing water at food factories, measure the flow rate of cooling water containing iron powder at ironworks, measure the flow rate at waterworks and sewerage, etc. Is used.
In a conventional ultrasonic vortex flowmeter, a vortex generator extending in a direction perpendicular to the flow direction is provided in a flow path through which a fluid to be measured flows, and one or two sets of vortex generators are provided downstream of the vortex generator. An ultrasonic sensor is provided to detect Karman vortices generated downstream of the vortex generator (see, for example, Patent Document 1). In such an ultrasonic flow meter, one set of ultrasonic sensors is provided in the flow path so as to face each other, one is a transmission side that transmits ultrasonic waves, and the other is in the fluid to be measured. It becomes the receiving side which receives the ultrasonic wave which propagated.

In this type of ultrasonic vortex flowmeter, an ultrasonic reception signal propagated through a Karman vortex generated alternately in proportion to the flow velocity in the flow path and received on the transmission side. The Doppler effect that the ultrasonic wave receives from the Karman vortex is detected as a sinusoidal phase modulation amount (vortex signal).

In addition, in an ultrasonic vortex flowmeter using two sets of ultrasonic sensors, by comparing the phases of two ultrasonic signals that propagate the fluid from the opposite directions relative to the Karman vortex flow, Only the phase change as a phase modulation amount received from the Karman vortex is extracted by canceling the influence of the sound velocity change of the fluid to be measured.

The conventional ultrasonic vortex flowmeter configured as described above is theoretically configured to extract the Doppler effect received by the ultrasonic wave from the Karman vortex as a phase change, so that it is independent of the type of fluid being measured. Vortices can be detected.
However, generally, disturbance noise received from flow noise, pipe vibration, or the like is superimposed on the vortex signal.

JP 2004-286673 A

The ultrasonic vortex flowmeter is easily affected by bubbles due to a difference in propagation speed between the ultrasonic gas and the liquid when bubbles are present in the fluid to be measured. Therefore, not only disturbance noise but also large noise received from bubbles is superimposed on the vortex signal in the fluid, and there is a possibility that the Karman vortex cannot be detected when a large amount of large bubbles are mixed.

With respect to such a problem, the invention of Patent Document 1 uses a tracking filter that determines the cutoff frequency of a filter to be applied to the vortex signal from the frequency of the vortex pulse obtained by zero-crossing the vortex signal. I'm getting a clean sine wave.

In this case, since the vortex pulse is affected by bubbles, there is an error between the vortex pulse and the true vortex frequency. Therefore, the pass band of the tracking filter for removing noise due to the influence of bubbles in the final stage is set to be relatively wide so that the original vortex frequency does not deviate from that band.

However, for that purpose, noise is measured in addition to the original signal. When noise larger than the amplitude of the vortex signal is superimposed with the passage of bubbles, an error pulse is output. In addition, when a bubble large enough to block the propagation of the ultrasonic wave passes, the reception voltage cannot be secured, resulting in a problem that the vortex pulse is lost. As a result, a situation such as generation of an output error or output stop occurs. Therefore, it is necessary to detect bubbles and reflect the result in the flow rate measurement.
Therefore, an object of the present invention is to provide an ultrasonic vortex flowmeter in which the above-mentioned problems are solved and bubble resistance is improved by detecting bubbles in addition to the conventional configuration.

In order to solve the above problems, the present invention has the following features.
The invention according to claim 1 includes a flow meter body in which a flow path through which a fluid to be measured flows is formed,
A vortex generator provided in the flow path so as to be orthogonal to the flow direction;
An ultrasonic transmitter that transmits ultrasonic waves by a transmission signal of a predetermined period;
An ultrasonic receiver for receiving the ultrasonic wave transmitted from the ultrasonic transmitter;
Using the received signal affected by the Karman vortex generated downstream of the vortex generator received by the ultrasonic receiver, a vortex signal indicating a phase modulation amount generated in the received signal due to the generation of the Karman vortex Vortex signal generating means for generating;
And at least
Filter means provided between the vortex signal generation means and the calculation means, and allows a frequency in a predetermined frequency band to pass through;
Reading out a frequency band corresponding to the diameter of the flow passage of the flow meter body from the storage means, and setting means for setting a cutoff frequency of the filter based on the frequency band,
A calculation means for calculating the flow rate of the fluid under measurement from the period of the vortex signal generated by the vortex signal generation means;
In the ultrasonic vortex flowmeter consisting of
The computing means further includes:
A bubble detector for detecting the presence or absence of bubbles based on the amplitude value of the vortex signal;
Storage means for storing a threshold for determining the presence or absence of the bubble, and the bubble detection unit is connected to the setting means and the storage means.

In the ultrasonic vortex flowmeter according to the first aspect, the pass band of the filter means when there is no bubble is a frequency corresponding to the minimum flow rate to the maximum flow rate of the flow meter. In addition, the pass band of the filter means when there is a bubble is a frequency before the measurement.

According to the invention of claim 1, by detecting the presence or absence of bubbles from the vortex signal, the frequency of the vortex signal when there is no bubble can be used to calculate the cutoff frequency that determines the band of the filter. The output error at the time of mixing can be reduced.

According to the invention of claim 2, by detecting the presence or absence of bubbles from the vortex signal, the frequency of the vortex signal when there is no bubble can be used to calculate the cutoff frequency that determines the band of the filter. Therefore, it is possible to reduce the probability of output stop and erroneous output due to the vortex frequency deviating from the pass band of the band pass filter due to a sharp change in flow rate.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a block diagram showing a circuit configuration of an embodiment of an ultrasonic vortex flowmeter according to the present invention.
As shown in FIG. 1, the ultrasonic vortex flowmeter 10 includes a flowmeter body 14 having a flow path 12 through which the fluid to be measured flows, and a flow of the fluid to be measured in the flow path 12 of the flowmeter body 14. And a vortex generator 16 extending in a vertical direction perpendicular to a direction (indicated by an arrow in FIG. 1). The vortex generator 16 has a substantially pentagonal cross section when viewed from above.

Then, in the process in which the fluid to be measured flows downstream while colliding with the vortex generator 16 facing the upstream side, Karman vortices 17 are alternately generated on the left and right sides of the vortex generator 16. Since the frequency of the Karman vortex 17 is proportional to the flow velocity of the fluid to be measured, the flow velocity of the fluid to be measured is obtained by detecting the number of Karman vortices 17 generated in the fluid to be measured. Calculate the flow rate.

There are various sizes of the ultrasonic vortex flowmeter 10 and there are various sizes of the upstream end face of the vortex generator (the size of the vortex generator). The diameter and the size of the vortex generator are proportional to each other, that is, the size of the vortex generator is set to increase in proportion to the increase in the diameter.

Next, the detailed structure of the ultrasonic vortex flowmeter 10 of the present embodiment will be described below.
The ultrasonic transmitter 20 and the ultrasonic receiver 22 are attached to the inner wall of the flow path on the downstream side of the vortex generator 16 of the flow meter body so as to face each other. The ultrasonic transmitter 20 and the ultrasonic receiver 22 have an ultrasonic sensor made of a piezoelectric element. When a drive signal is input from the drive circuit 24 to the ultrasonic transmitter 20, the ultrasonic transmitter The ultrasonic wave transmitted from 20 propagates through the fluid to be measured flowing through the flow path 12 and is received by the ultrasonic receiver 22.

Then, in the process in which the fluid to be measured flows downstream while colliding with the vortex generator 16, the Karman vortex 17 is disposed on the downstream side of the vortex generator 16 in a cycle proportional to the flow velocity of the fluid to be measured flowing in the flow path 12. It occurs on the left and right. At that time, the ultrasonic wave propagating in the flow path 12 is modulated in the process of passing through the Karman vortex 17 generated downstream of the vortex generator 16. Therefore, the generation frequency (vortex signal) of the Karman vortex 17 is detected from the phase difference between the detection signal output from the ultrasonic receiver 22 and the drive signal, and the fluid to be measured flowing in the flow path 12 is detected based on this frequency. Measure the flow rate.

The ultrasonic transmitter 20 and the ultrasonic receiver 22 are connected to the flow rate calculation unit 26. The flow rate calculation unit 26 passes through the flow path 12 based on the frequency of the Karman vortex 17 obtained from the phase difference between the drive signal input to the ultrasonic transmitter 20 and the received signal output from the ultrasonic receiver 22. Calculate the flow rate of the fluid to be measured.

The flow rate calculation unit 26 includes the drive circuit 24, the reception circuit 28, the phase comparison circuit 29 (vortex signal generation means), the filter amplifier circuit (amplification circuit) 30, the comparator circuit 32, and the calculation circuit 34. The arithmetic circuit (CPU) 34 includes an A / D conversion unit 36, a band pass filter unit (BPF unit) 38 (filter), a counter unit 40, a frequency setting unit 42 (setting unit), a memory 44 (storage unit), It has a flow rate integration unit 46 (calculation means), an AD conversion unit 60, and a bubble detection unit 61, and performs bandpass filter processing, filter cutoff frequency calculation processing, and flow rate calculation.

The drive circuit 24 has an oscillator that outputs an excitation signal having a constant period, and outputs a drive signal in which the voltage is changed to a sine wave based on the excitation signal from the oscillator to the ultrasonic transmitter 20.

When receiving the ultrasonic signal propagated through the flow path 12, the ultrasonic receiver 22 outputs the received signal to the receiving circuit 28. In the reception circuit 28, the reception signal is amplified and output to the phase comparison circuit 29. Then, the phase comparison circuit 29 generates a signal (vortex signal) indicating a phase difference between the drive signal output from the drive circuit 24 and the reception signal output from the reception circuit 28. The vortex signal output from the phase comparison circuit 29 is amplified by the filter amplifier circuit 30 and input to the A / D conversion unit 36 of the arithmetic circuit (CPU) 34 to be converted into a digital signal. (BPF section) 38 performs filtering.

Further, the vortex signal output from the phase comparison circuit 29 is zero-cross-comparated by the comparator circuit 32 and converted into a binary signal (vortex pulse signal) consisting only of a high level and a low level, and is sent to the counter unit 40. Entered. The counter unit 40 measures the frequency of the vortex pulse signal.

The signal from the filter amplifier circuit 30 is input to the A / D conversion unit 60, converted into a digital signal, and then input to the bubble detection unit 61. Then, it is constantly monitored whether the amplitude value of the A / D converted vortex signal is equal to or greater than a threshold value (stored in the memory 44 for each diameter of the flow meter). Is output to the frequency setting unit 42.

The frequency setting unit 42 of the arithmetic circuit (CPU) 34 is measured by the data stored in the memory 44 (individual information for each flow meter such as the diameter of the flow meter and the flow range (vortex frequency range)) and the counter unit 40. Based on the frequency of the vortex pulse signal, the cut-off frequency of the bandpass filter unit 38 that passes the vortex signal is set.

In the memory 44 (storage means), the frequency range (vortex frequency range) of the vortex signal that should be passed in correspondence with the diameter of the flow meter, the threshold value when detecting bubbles and stopping frequency measurement, the flow rate Individual information (for example, frequencies corresponding to each of the minimum flow rate to the maximum flow rate) such as a flow rate measurable range that can be measured by the meter is registered in advance.

Further, when the diameter of the flow meter is designated, the frequency setting unit 42 reads individual information including the vortex frequency range corresponding to the diameter from the memory 44, and uses the vortex frequency range as the cutoff frequency of the bandpass filter unit 38. This is set as the range.

As a signal input to the bandpass filter unit 38, the cutoff frequency when there are no bubbles in the fluid to be measured is a frequency corresponding to each of the minimum flow rate to the maximum flow rate determined by the diameter of the flow meter (respectively fmin and fmax).
The cutoff frequency in the case where bubbles are present in the fluid to be measured is from a frequency obtained by multiplying the measured vortex frequency by a coefficient n to a frequency obtained by multiplying the coefficient m (m> n).
Further, when a signal indicating that there is a bubble is output from the bubble detection unit 61 (that is, as described above, the amplitude value of the vortex signal obtained by the bubble detection unit 61 being A / D converted by the A / D conversion unit 60. When it is determined that the value exceeds the threshold value), the measurement of the eddy frequency is stopped, and the value of the immediately preceding cutoff frequency is adopted as the value in between. And when there is no bubble, frequency measurement is restarted.

Therefore, in the arithmetic circuit (CPU) 34, the vortex signal A / D converted by the A / D converter 36 is subjected to tracking bandpass filter processing by the BPF unit 38 based on the cutoff frequency set above. After that, the flow rate calculation unit 46 converts and integrates into a pulse train to calculate the flow rate, and outputs a flow rate signal to the output terminal 47. In addition, the conversion method to a pulse train is performed by performing zero cross comparison with a small hysteresis.

In FIG. 2, the relationship between the presence / absence of bubbles and the cutoff frequency (= pass band) will be described. The horizontal axis shows the measurement time, and the vertical axis shows the phase difference signal voltage (output of the phase detection circuit 29) as a vortex signal. As can be seen from FIG. 2, the presence or absence of bubbles is determined by whether or not there is a frequency value measured between the upper and lower dotted lines U and L of the bubble detection determination value. U and L are set experimentally.

In FIG. 2, when there is a bubble at first, if the pass band of the bandpass filter exceeds the threshold and becomes A (n times to m times the vortex frequency), the frequency measurement is stopped simultaneously. When the band A is changed to the band B and bubbles disappear, the pass band of the band-pass filter is B (frequency corresponding to each of the minimum flow rate fmin to the maximum flow rate fmax), and the frequency measurement is resumed. In the figure, a case where the band is further measured as A → B → A → B is shown. The relationship between the frequency bands A and B is shown in FIG. 3, and the band A is set in the range of 0.7 to 1.3 times the vortex frequency fc.

Next, the control flow of the present invention will be described with reference to FIG.
First, since the vortex frequency is not measured immediately after the power is turned on, the pass band is set to the above-described fmin to fmax (step S1).
In step S2, the bubble detector 61 is used to determine whether or not the amplitude value of the vortex signal A / D converted by the A / D converter 60 is equal to or greater than a threshold value, thereby confirming the presence or absence of bubbles (specifically If not, the time constant is first returned (step S3), and the passband is again set to fmin to fmax (step S3). Then, the vortex frequency is measured using the frequency setting unit 42 at a constant cycle (here, 30 ms cycle) (step S5), and the flow rate is calculated (step S10).

  When it is determined in step S2 that there are bubbles, the time in which bubbles are continuously mixed is confirmed in step S6. Here, it is checked whether or not 500 ms is continued. If the duration is less than 500 ms (NO) (step S7), the passband is set to n times to m times (here, 0.7 times to 1.3 times) the vortex frequency measured most recently. Then, the flow rate is calculated (step S10).

If the mixing continues for 500 ms or longer in step S6 (step 8), the pass band is set to fmin to fmax.
In the present invention, the measurement of the vortex frequency is not performed when bubbles are mixed. Therefore, even if the flow rate changes when bubbles are mixed, the passband cannot be reset. In this case, the vortex frequency may be out of the pass band, and as a result, output may be stopped or erroneous output may be caused. For this reason, a passband is expanded and such a situation is avoided.
In this state, since the noise removal effect is low and the output is violated due to the influence of bubbles, the time constant should be set longer only when a short time constant is set for the purpose of stabilizing the output. Note that here (3 seconds, step 9). Then, the flow rate is calculated (step S10).

  In the above embodiment, the detection of bubble contamination is processed by software in the arithmetic circuit, but by determining the amplitude threshold as a circuit element and performing comparison processing, a bubble contamination detection signal is generated from the hardware, It is possible to detect bubbles even if they are input to the arithmetic circuit by interruption. Furthermore, the tracking filter may be configured as hardware.

It is a block diagram which shows the circuit structure of one Example of the ultrasonic vortex flowmeter which becomes this invention. The output of the phase difference circuit 29 of FIG. 1 when the fluid to be measured is measured by the ultrasonic vortex flowmeter of the present invention is shown. It is a figure which shows the relationship between the bands A and B shown in FIG. It is a figure which shows the control flow which shows the method of the band setting in the band pass filter in FIG. 1 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Ultrasonic vortex flowmeter 12 Flow path 14 Flowmeter main body 16 Vortex generator 17 Karman vortex 20 Ultrasonic transmitter 22 Ultrasonic receiver 24 Drive circuit 26 Flow rate calculation part 28 Reception circuit 29 Phase comparison circuit (vortex signal generation means )
32 Comparator circuit 34 Arithmetic circuit 36 A / D converter 38 Band pass filter (filter)
40 Counter unit 42 Frequency setting unit (setting means)
44 Memory (storage means)
46 Flow rate integration unit (calculation means)
60 A / D converter 61 Bubble detection unit

Claims (2)

A flow meter body in which a flow path for the fluid to be measured is formed;
A vortex generator provided in the flow path so as to be orthogonal to the flow direction;
An ultrasonic transmitter that transmits ultrasonic waves by a transmission signal of a predetermined period;
An ultrasonic receiver for receiving the ultrasonic wave transmitted from the ultrasonic transmitter;
Using the received signal affected by the Karman vortex generated downstream of the vortex generator received by the ultrasonic receiver, a vortex signal indicating a phase modulation amount generated in the received signal due to the generation of the Karman vortex Vortex signal generating means for generating;
And at least
Filter means provided between the vortex signal generation means and the calculation means, and allows a frequency in a predetermined frequency band to pass through;
Reading out a frequency band corresponding to the diameter of the flow passage of the flow meter body from the storage means, and setting means for setting a cutoff frequency of the filter based on the frequency band,
A calculation means for calculating the flow rate of the fluid under measurement from the period of the vortex signal generated by the vortex signal generation means;
In the ultrasonic vortex flowmeter consisting of
The computing means further includes:
A bubble detector for detecting the presence or absence of bubbles based on the amplitude value of the vortex signal;
Storage means for storing a threshold value for determining the presence or absence of the bubbles,
The ultrasonic vortex flowmeter, wherein the bubble detection unit is connected to the setting means and storage means. The pass band of the filter means when there is no bubble is a frequency corresponding to the minimum flow rate to the maximum flow rate of the flow meter, and the pass band of the filter means when there is a bubble is the frequency before the measurement. The ultrasonic vortex flowmeter according to claim 1, wherein the ultrasonic vortex flowmeter is provided.

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